Resolution Calculator

How to use the resolution calculator

1. Fill in the fields — they start with a worked example.
2. Read the answer, and the arithmetic shown beneath it.
3. Copy the results, or adjust the inputs to compare scenarios.

About this tool

This is the print size calculation run backwards. Instead of asking how large a file can print, it asks what a file must contain to print at a size you have already chosen. Multiply each dimension in inches by the target resolution and you have the pixel count you need to supply.

It answers the question that comes up when someone commissions work: an A2 poster at 300 PPI needs roughly 4960 × 7016 pixels, which is about 35 megapixels. Knowing that before the shoot is much cheaper than discovering it afterwards, because no amount of processing recovers detail that was never recorded.

300 PPI is the print industry's habit rather than a law of physics. It comes from a 150 line-per-inch halftone screen at two samples per line, and it holds for anything read at arm's length. Viewing distance is the real variable: a billboard is often produced at 15 PPI and looks perfect from the road.

So the target resolution field matters as much as the size. Dropping from 300 to 150 PPI quarters the pixels required, because the requirement scales with area rather than with width. That single fact decides whether a job needs a medium-format camera or a phone.

Common uses

• Specifying the minimum file size to a photographer or illustrator before a shoot.
• Checking whether an existing camera has enough megapixels for a planned print.
• Sizing an export from a design tool so the printer does not resample it.

Frequently asked questions

How many megapixels do I need to print A2?

About 35 megapixels for 300 PPI, or roughly 9 megapixels at 150 PPI, which is enough for a poster viewed from a metre away.

What is the difference between DPI and PPI?

PPI counts image pixels per inch; DPI counts ink dots a printer lays down per inch. Printers use several dots to reproduce one pixel, so a 300 PPI file is normal on a 1440 DPI printer.

Why does halving the resolution quarter the file size?

Because pixels are counted over an area. Halving the pixels per inch halves both width and height, and half times half is a quarter.